Mixed phosphatic fertilizer and process for producing the same

ABSTRACT

In producing a mixed phosphatic fertilizer, humic acid is mixed with fused phosphate to cause the humic acid to react on alkaline ingredients of the fused phosphate for turning these alkaline ingredients into chelate compounds, so that water-soluble phosphoric acid contents of succeedingly added phosphatic fertilizers such as calcium superphosphate and calcium triple-superphosphate are not reduced or insolubilized by being reacted with such alkaline ingredients. Thus, unlike the prior art, a stabilized predetermined level of water-soluble phosphoric acid contents can be secured in the resultant mixed phosphatic fertilizer along with a predetermined level of citric acid-soluble phosphoric acid contents.

This is a continuation of application Ser. No. 338,078 filed Jan. 8,1982 which in turn is a divisional of U.S. Ser. No. 333,441 filed Dec.22, 1981, now U.S. Pat. No. 4,440,560 which is a continuation of U.S.Ser. No. 185,741 filed Sept. 10, 1980, now abandoned.

The present invention relates to a mixed phosphatic fertilizer havingboth water-soluble and citric acid-soluble phosphoric acid contents aswell as to a process for producing such a mixed phosphatic fertilizerand, more specifically, it relates to such a mixed phosphatic fertilizerhaving a stabilized predetermined level of such water-soluble phosphoricacid contents and a process for producing the same.

Fused phosphate, a typical phosphatic fertilizer, is generally producedby melting a mixture of about 100 parts by weight of phosphate rock andabout 90 parts by weight of serpentine at about 1400° C., water-coolingthe resultant molten mixture to obtain a vitreous matter and thengrinding the vitreous matter to fine mesh. Since fused phosphate isuseful for fertilization of volcanic ash soil or the like soils having ahigh phosphoric acid absorption coefficient due to its citricsolubility, its demand and consumption has been increasing in recentyear. However, since the citric solubility of phosphoric acid contentsof fused phosphate tends to deter the development or revelation of itsfertilizing effect, it has been proposed to mix fused phosphate withcalcium superphosphate, calcium triple-superphosphate or the likefertilizers having water-soluble phosphoric acid for compensating such atendency.

Nevertheless, since fused phosphate contains such alkaline ingredientsas 28-30% by weight of CaO and 17-20% by weight of MgO, thewater-soluble phosphoric acid contents will react with these alkalineingredients to produce water-insoluble contents (hereinafter thisreaction shall be referred to as reduction or insolubilization) so longas any phosphatic fertilizers having such water-soluble phosphoric acidcontents are merely added to the fused phosphate. Therefore, in order tosecure a predetermined level of water-soluble phosphoric acid contentsin a mixed phosphatic fertilizer, an excessively large quantity ofcalcium superphosphate, calcium triple-superphosphate or the likefertilizers having water-soluble phosphoric acid contents must be addedto fused phosphate. Further, the extent of such insolubilization ofwater-soluble phosphoric acid contents is greatly affected by grain sizedistribution or major grain sizes of fused phosphate. That is to say, asthe grain size of fused phosphate increases, the water-solublephosphoric acid contents of the resultant mixed phosphatic fertilizertend to undergo a higher degree of insolubilization or reduction.Besides, the resultant mixed phosphatic fertilizer undergoes a gradualinsolubilization of its water-soluble phosphoric acid contents duringits storage. Under these circumstances, it is difficult to secure astabilized predetermined level of water-soluble phosphoric acid contentsin the resultant mixed phosphatic fertilizer.

Accordingly, an object of the present invention is to provide a mixedphosphatic fertilizer having an improved fertilizing effect in which astabilized predetermined level of water-soluble phosphoric acid contentsis secured along with a predetermined level of citric acid-solublephosphoric acid contents, because such phosphoric acid contents areprevented from being reduced or insolubilized.

Another object of the present invention is to provide such an improvedmixed phosphatic fertilizer comprising a mixture of fused phosphate as amain component and at least one component selected from a specific groupconsisting of calcium superphosphate, calcium triple-superphosphate andphosphoric acid, and at least 15% by weight of humic acid.

Still another object of the present invention is to provide such animproved mixed phosphatic fertilizer comprising a mixture of 80-98 partsby weight of fused phosphate and 20-2 parts by weight of a componentselected from the specific group consisting of calcium superphosphate,calcium triple-superphosphate and phosphoric acid, and at least 15% or,more preferably, 20-50% by weight of humic acid.

Yet another object of the present invention is to provide a process forproducing such an improved mixed phosphatic fertilizer.

The humic acid herein referred to is obtained by a well-known process.That is to say, it is produced by grinding young coal such as lignite,brown coal or peat moss, and then oxidizing and decomposing the thusground young coal in the presence of nitric acid.

As is well-known, such humic acid as mentioned above shows a high cationexchange capacity in soil.

According to the present invention, such humic acid is added to amixture of well-known fused phosphate and the aforementioned phosphaticfertilizers having water-soluble phosphoric acid contents in an amountof at least 15% or, more preferably 20-50% by weight on a resultantmixture quantity basis in a mixer under hard agitation for securing asufficient reaction. Since this reaction is accomplished solid to solid,it is preferable to add, as a reaction medium, 20-30% by weight of waterbased on the first-cited mixture. Although it is not necessary tospecially heat the reaction system, heating is effective to acceleratethe reaction.

As a result of the foregoing reaction, alkalis such as calcium andmagnesium contained in the fused phsophate react with radicals of thehumic acid to produce chelate compounds. Of course, such alkalis can beefficiently utilized as citric acid-soluble lime and magnesia when theresultant mixture is applied to the soil.

Then, at least one fertilizer selected from the group consisting ofcalcium superphosphate, calcium triple-superphosphate and phosphoricacid is added. Since such alkaline ingredients of the fused phosphate asCaO are masked as a result of the reaction with humic acid initiallyadded thereto as described previously, the water-soluble phosphoric acidcontents of the aforementioned phosphatic fertilizers such as calciumsuperphosphate cannot react with these alkaline ingredients of the fusedphosphate any more. Thus, unlike the prior art mixed phosphaticfertilizers, the water-soluble phosphoric acid contents are neitherinsolubilized nor fixed at all. Therefore, according to the presentinvention, a mixed phosphatic fertilizer having a predetermined level ofwater-soluble phosphoric acid contents as against a predetermined levelof citric acid-soluble phosphoric acid contents can readily be obtainedby mixing with a predetermined quantity of fused phosphate at least onephosphatic fertilizer such as calcium superphosphate in a precalculatedquantity equivalent to the aforesaid predetermined level ofwater-soluble phosphoric acid contents.

It is to be noted here that according to the present invention thephosphatic fertilizers having water-soluble phosphoric acid contentssuch as calcium superphosphate may be added to fused phosphatesimultaneously with humic acid so long as the latter is added thereto,although such a simultaneous addition any more or less kill the effectof the humic acid to prevent insolubilization of water-solublephosphoric acid contents during the course of mixing the feed materials.In this case also, the cation exchange capacity of humic acid iseffective to selectively react the same with the alkaline ingredients ofthe fused phosphate to produce chelate compounds and, thus, to preventthe simultaneously added water-soluble phosphoric acid contents frombeing reacted with these alkaline ingredients to be insolubilized.

As described herein-above, the present invention provides an improvedprocess comprising mere an addition of humic acid for producing animproved mixed phosphatic fertilizer which comprises mere a mixture offused phosphate thus treated with humic acid and at least one componentselected from the specific group consisting of calcium superphosphate,calcium triple-superphosphate and phosphoric acid. Nevertheless, themixed phosphatic fertilizer according to the present invention haswater-soluble phosphoric acid contents in a very stabilized form whichare substantially free from the effect of the grain size of fusedphosphate and which are not decreased by or reduction even after a longperiod of storage.

Further, the humic acid used according to the present invention not onlyfunctions as a soil conditioner as is well-known, but also is effectiveto diffuse and infiltrate alkaline ingredients into soil. Thus, themixed phosphatic fertilizer according to the present invention canexhibit a fertilizing effect remarkably improved over that of the priorart mixed phosphatic fertilizers due to synergistic effects of itsstabilized predetermined citric acid-soluble and water-solublephosphoric acid contents in combination with humic acid having theaforementioned effects.

These and other objects and features of the present invention will beobvious from the following detailed description of the invention whichwill be best understood when read in connection with the accompanyingdrawing, in which:

FIG. 1 is a chart showing curves of water-soluble phosphoric acidcontents of several mixed phosphatic fertilizers plotted against lapseof time.

EXPERIMENT 1 (1) Feed materials

                                      TABLE 1                                     __________________________________________________________________________                  Phosphoric acid contents (wt. %)                                                             Acid-insoluble                                                 P.sub.2 O.sub.5                                                                              alkali-soluble                                   Feed Materials                                                                              S--P.sub.2 O.sub.5                                                                 C--P.sub.2 O.sub.5                                                                 W--P.sub.2 O.sub.5                                                                 contents                                         __________________________________________________________________________    Fused phosphate                                                                             --   21.3 tr.  --                                               (commercially available)                                                      Calcium       44.4 --   40.2 --                                               triple-superphosphate                                                         (commercially available)                                                      Humic acid (Produced by                                                                     --   --   --   *80                                              Japan Metals & Chemical                                                       Co., Ltd.)                                                                    __________________________________________________________________________     Notes:                                                                        (1)S-- P.sub.2 O.sub.5 denotes soluble phosphoric acid content; C--P.sub.     O.sub.5 citric acidsoluble phosphoric acid content; and W--P.sub.2 O.sub.     watersoluble phosphoric acid content. The same shall apply hereinafter.       (2)*Content (as dry) insoluble in 3.5% but hydrochloric acid soluble in 1     aqueous solution of sodium hydroxide.                                    

The foregoing feed materials were put into a blending mixer by therespective sample formulations No. 1 through 20 given in Table 2. Thethus fed raw materials were mixed therein for a sufficient reaction inthe presence of about 20-30% by weight of water based on the respectivefeedstock weights. The resultant samples were analyzed for their citricacid-soluble and water-soluble phosphoric acid contents, the results ofwhich are given in Table 3 as contrasted to their theoretical levelsbefore mixing and reaction. In Tables 2 and 3, samples No. 7 through 20each represent a mixing formulation according to the present invention.

                  TABLE 2                                                         ______________________________________                                        Mixing formulation humic acid                                                 Mixing formulation humic acid                                                 Sample              Calcium                                                   No.    Fused phosphate                                                                            triple-superphosphate                                                                        Humic acid                                 ______________________________________                                        1      95           5              --                                         2      90           10             --                                         3      80           20             --                                         4      70           30             --                                         5      60           40             --                                         6      95           5              11.12 (10)                                 7      95           5              17.65 (15)                                 8      95           5              25.00 (20)                                 9      95           5              33.33 (25)                                 10     95           5              42.85 (30)                                 11     95           5              53.85 (35)                                 12     95           5              66.67 (40)                                 13     95           5              100.00 (50)                                14     95           5              150.00 (60)                                15     90           10             17.65 (15)                                 16     90           10             25.00 (20)                                 17     90           10             42.85 (30)                                 18     90           10             66.67 (40)                                 19     80           20             25.00 (20)                                 20     80           20             66.67 (40)                                 ______________________________________                                    

Parenthesized numerals each show a percentage based on the total weightof each mixed fertilizer sample.

                                      TABLE 3                                     __________________________________________________________________________    Analyzed citric acid-soluble and water-soluble phosphoric acid contents       Theoretical level (wt. %)                                                                              Analyzed level (wt. %)                                                W--P.sub.2 O.sub.5 W--P.sub.2 O.sub.5                                                                    Effective W--P.sub.2 O.sub.5      Sample No.                                                                          C--P.sub.2 O.sub.5                                                                 W--P.sub.2 O.sub.5.sup.(a)                                                          C--P.sub.2 O.sub.5 × 100                                                        C--P.sub.2 O.sub.5                                                                 W--P.sub.2 O.sub.5.sup.(b)                                                          C--P.sub.2 O.sub.5 × 100                                                        content b/a                       __________________________________________________________________________                                                × 100)                      1     22.45                                                                              2.01  8.95    22.43                                                                              0.30  1.34    14.93                             2     23.61                                                                              4.02  17.03   23.56                                                                              0.61  2.59    15.17                             3     25.92                                                                              8.04  31.02   25.89                                                                              1.23  4.06    15.31                             4     28.23                                                                              12.06 42.72   28.19                                                                              1.87  6.63    15.51                             5     30.54                                                                              16.08 52.65   30.64                                                                              2.51  8.19    15.61                             6     20.21                                                                              1.81  8.96    20.16                                                                              0.84  4.17    46.41                             7     19.03                                                                              1.70  5.93    18.98                                                                              1.34  7.06    78.91                             8     17.96                                                                              1.61  8.96    17.89                                                                              1.44  8.05    89.56                             9     17.10                                                                              1.53  8.95    17.11                                                                              1.47  8.59    96.31                             10    16.33                                                                              1.46  8.94    16.34                                                                              1.54  9.42    105.31                            11    15.62                                                                              1.40  8.96    15.66                                                                              1.63  10.41   116.31                            12    14.97                                                                              1.34  8.95    14.95                                                                              1.64  10.97   122.31                            13    13.82                                                                              1.24  8.97    13.80                                                                              1.63  11.81   131.46                            14    8.98 0.80  8.91    8.79 1.06  12.06   132.50                            15    20.01                                                                              3.41  17.04   20.10                                                                              2.50  12.43   73.26                             16    18.89                                                                              3.22  17.05   18.99                                                                              2.84  14.96   88.31                             17    17.17                                                                              2.92  17.01   17.21                                                                              2.89  16.79   98.91                             18    15.74                                                                              2.68  17.03   15.76                                                                              2.77  17.58   103.26                            19    20.74                                                                              6.43  31.00   20.69                                                                              4.52  21.85   70.29                             20    17.28                                                                              5.36  31.02   17.31                                                                              5.29  30.56   98.65                             __________________________________________________________________________

As understood from Table 3, those samples having no humic acid content(Samples No. 1 through 5) obviously undergo insolubilization of theirwater-soluble phosphoric acid contents to such an extent that theresultant mixed phosphatic fertilizers contain only about 15% by weightof input water-soluble phosphoric acid contents. Thus, such formulationshaving no humic acid content show an extremely low yield ofwater-soluble phosphoric acid contents.

However, the formulations according to the present invention(represented by Samples No. 7 through 20) undergo remarkably smallinsolubilization of such water-soluble phosphoric acid contents, also asshown in Table 3. Further, as the humic acid content of the feed mixtureformulation increases, the effective water-soluble phosphoric acidcontents of the resultant mixed phosphatic fertilizer increaseproportionately. However, with a humic acid content of 10% by weight,the resultant mixed phosphatic fertilizer has an effective water-solublephosphoric acid content lower than a half, namely, only 46%. Thus, it ispreferred that the feed mixture formulation contains at least 15% byweight of humic acid. In the meantime, with a humic acid content of thefeed mixture formulation, its additional increase does not significantlycontribute to the effective water-soluble phosphoric acid content anymore, but acts to decrease the citric acid-soluble phosphoric acidcontents. Thus, a mixture containing such an excessive quantity of humicacid will more or less lose its practicability as a fertilizer. In thissense, it is preferred that the feed mixture contains from about 15% toabout 50% by weight of humic acid.

EXPERIMENT 2

Samples No. 1, 8, 10 and 12 of Experiment 1 were analyzed to determinechanges in water-soluble phosphoric acid contents during the course oftheir preparation and with lapse of time thereafter, the results ofwhich are shown in FIG. 1. As understood from FIG. 1, the mixedphosphatic fertilizer having no humic acid content (Sample No. 1)undergoes during the course of its preparation a remarkable reduction orinsolubilization of its water-soluble phosphoric acid contents as aresult of mixing or reaction of fused phosphate and calciumtriple-superphosphate. Thus, its water-soluble phosphoric acid contentsare not only lost remarkably during the course of its preparation, butalso gradually decreased with lapse of time after the preparation.While, the mixed phosphatic fertilizers according to the presentinvention show an extremely small insolubilization of or, conversely,even a samll increase in their water-soluble phosphoric acid contentsduring the course of their preparation. Besides, they retain almost thesame levels of water-soluble phosphoric acid contents as those observedupon their preparation even after one year of storage withoutsignificant changes with time. This means that the mixed phosphaticfertilizers according to the present invention have a very stablequality with their water-soluble phosphoric acid contents securable overa long period after production.

EXPERIMENT 3

In this experiment, instead of calcium triple-superphosphate ofExperiment 1, there was used a phosphoric acid source which was acommercially available 45% (as H₃ PO₄) aqueous solution of phosphoricacid. Then, Samples No. 1 through 15 were prepared in the same manner asin Experiment 1 by using formulations shown in Table 4. The resultantmixed phosphatic fertilizer samples were subjected to analysis, theresults of which are summarized in Table 5. In this experiment, SamplesNo. 5 through 15 represent the formulations according to the presentinvention.

                  TABLE 4                                                         ______________________________________                                        Mixing formulation                                                            Mixing formulation (wt. %)                                                    Sample              Aqueous phosphoric                                        No.    Fused phosphate                                                                            acid solution (as P.sub.2 O.sub.5)                                                           Humic acid                                 ______________________________________                                        1      98           2              --                                         2      95           5              --                                         3      90           10             --                                         4      85           15             --                                         5      98           2              17.65 (15)                                 6      98           2              25.00 (20)                                 7      98           2              42.85 (30)                                 8      98           2              66.67 (40)                                 9      98           2              100.00 (50)                                10     95           5              25.00 (20)                                 11     95           5              42.85 (30)                                 12     95           5              66.67 (40)                                 13     95           5              100.00 (50)                                14     90           10             25.00 (20)                                 15     90           10             66.67 (40)                                 ______________________________________                                    

                                      TABLE 5                                     __________________________________________________________________________    Analyzed citric acid-soluble and water-soluble phosphoric acid content        Theoretical level (wt. %)                                                                              Analyzed level (wt. %)                                                W--P.sub.2 O.sub.5 W--P.sub.2 O.sub.5                                                                    Effective W--P.sub.2 O.sub.5      Sample No.                                                                          C--P.sub.2 O.sub.5                                                                 W--P.sub.2 O.sub.5.sup.(a)                                                          C--P.sub.2 O.sub.5 × 100                                                        C--P.sub.2 O.sub.5                                                                 W--P.sub.2 O.sub.5.sup.(b)                                                          C--P.sub.2 O.sub.5 × 100                                                        content (b/a                      __________________________________________________________________________                                                × 100)                      1     22.71                                                                              1.99  8.8     22.74                                                                              0.16  0.70    8.26                              2     24.82                                                                              4.91  19.8    24.70                                                                              0.52  2.10    10.56                             3     28.10                                                                              9.64  34.3    26.94                                                                              1.10  4.08    11.37                             4     31.31                                                                              14.20 45.4    31.13                                                                              1.88  6.04    13.21                             5     19.25                                                                              1.69  8.78    19.31                                                                              1.41  7.30    83.67                             6     18.17                                                                              1.59  8.75    18.20                                                                              1.61  8.85    101.30                            7     16.52                                                                              1.45  8.78    16.49                                                                              1.72  10.43   118.51                            8     15.14                                                                              1.33  8.78    15.11                                                                              1.76  11.65   132.16                            9     13.98                                                                              1.22  8.73    13.89                                                                              1.62  11.66   132.79                            10    19.86                                                                              3.93  19.79   19.79                                                                              3.16  15.97   80.29                             11    18.05                                                                              3.57  19.78   18.10                                                                              3.40  18.78   95.26                             12    16.55                                                                              3.27  19.56   16.54                                                                              3.35  20.25   102.36                            13    15.27                                                                              3.02  19.78   15.30                                                                              3.74  24.44   123.86                            14    22.48                                                                              7.71  34.30   22.41                                                                              6.04  26.95   78.31                             15    18.73                                                                              6.43  34.33   18.70                                                                              5.49  29.36   85.37                             __________________________________________________________________________

As understood from Table 5, an aqueous solution of phosphoric acidreacts well on fused phosphate to such an extent that the effectivewater-soluble phosphoric acid contents of the resultant mixedphosphateic fertilizer are reduced to 8-13% of their input levels, asshown by Samples No. 1 through 4.

While, in the mixed phosphatic fertilizers according to the presentinvention represented by Samples No. 5 through 15, the effectivewater-soluble phosphoric acid contents are as high as 84% or aboveshowing an effect of humic acid to prevent insolubilization or reductionof such water-soluble phosphoric acid contents in mixing a phosphoricacid source and fused phosphate.

EXPERIMENT 4

In this experiment, in order to determine the effect of grain sizes offushed phosphate as an feed material, the same fused phosphate as thoseused in Experiments No. 1 and 2 has its grain sizes adjusted to up tomesh No. 16 on the one hand and above mesh No. 16 but up to mesh No. 100on the other, and the same experiment procedure as that of Experiment 1was repeated, the results of which are summarized in Table 6.

As understood from Table 6, those formulations without humic acidcontent undergo an increased reduction or solubilization ofwater-soluble phosphoric acid contents as the grain size of the feedfused phosphate increases,. Thus, without humic acid content, theresultant mixed phosphatic fertilizers have a remarkably decreasedeffective water-soluble phosphoric acid content.

While, the mixed phosphatic fertilizer products having the formulationsaccording to the present invention are hardly affected by the grainsizes of the feed fused phosphate, as shown in Table 6.

Thus, the process according to the present invention favorably featuresthat in producing mixed phosphatic fertilizers fused phosphate can bemixed with calcium superphosphate or the like phosphatic fertilizershaving water-soluble phosphoric acid contents without specially takinginto consideration the grain sizes of the fused phosphate.

EXPERIMENT 5

In this experiment, Komatsuna, a kind of Chinese cabbage, was ferilizedwith Samples No. 3, 7, 8, 10, 12 and 13 of Experiment 1 to determinetheir ferilizing effect, the results of which are summarized in Table 7.

                                      TABLE 6                                     __________________________________________________________________________    Effect of different grain sizes of fused phosphate                            Mixing formulation (wt. %)                                                                        Aqueous                                                                              Water-soluble phosphoric acid content                                         (W--P.sub.2 O.sub.5)                                           calcium phosphoric               Effective                              Fused triple- acid solution                                                                              Theoretical                                                                         Analyzed                                                                            W--P.sub.2 O.sub.5               Sample No.                                                                          phosphate                                                                           superphosphate                                                                        (as P.sub.2 O.sub.5)                                                                 Humic acid                                                                          level level content                          __________________________________________________________________________    1     A95    5      --     --    2.01  0.30  14.93                            2     B95    5      --     --    2.01  0.14  6.97                             3     A95    5      --     25.00(20)                                                                           1.61  1.44  89.56                            4     B95    5      --     25.00(20)                                                                           1.61  1.37  85.09                            5     A95    5      --     66.67(40)                                                                           1.21  1.48  122.31                           6     B95    5      --     66.67(40)                                                                           1.21  1.45  120.15                           7     A90   10      --     --    4.02  0.61  15.17                            8     B90   10      --     --    4.02  0.21  5.22                             9     A90   10      --     25.00(20)                                                                           3.22  2.84  88.31                            10    B90   10      --     25.00(20)                                                                           3.22  2.71  84.16                            11    A90   10      --     66.67(40)                                                                           2.41  2.49  103.26                           12    B90   10      --     66.67(40)                                                                           2.41  2.53  104.85                           13    A98   --      2      --    1.99  0.16  8.26                             14    B98   --      2      --    1.99  0.08  4.02                             15    A98   --      2      25.00(20)                                                                           1.59  1.61  101.30                           16    B98   --      2      25.00(20)                                                                           1.59  1.57  98.74                            17    A98   --      2      66.67(40)                                                                           1.19  1.57  132.16                           18    B98   --      2      66.67(40)                                                                           1.19  1.51  130.52                           19    A95   --      5      --    4.91  0.52  10.51                            20    B95   --      5      --    4.91  0.27  5.50                             21    A95   --      5      25.00(20)                                                                           3.93  3.16  80.29                            22    B95   --      5      25.00(20)                                                                           3.93  3.08  78.37                            23    A95   --      5      66.67(40)                                                                           2.95  3.02  102.36                           24    B95   --      5      66.67(40)                                                                           2.95  3.01  112.14                           __________________________________________________________________________     In the fused phosphate column, grain sizes up to mesh No. 16 are indicate     as A, and those up above No. 16 but up to 100 as B.                      

                                      TABLE 7                                     __________________________________________________________________________    Fertilizing effect analysis                                                                                  Analyzed phosphoric acid contents              Sample          Crop level (g./pot as dry)                                                                         Content                                                                            Absorption                                                                              percentage                No. Fertilized with:                                                                          Shoot                                                                             Index                                                                             Root                                                                             Index                                                                             Ration (%)                                                                          (mg/pot)                                                                           (mg/pot)                                                                            Index                                                                             utilization               __________________________________________________________________________        None added   8.46                                                                              57 1.20                                                                              79 0.80   70.03                                                                             --    --  --                            Fused phosphate                                                                           14.72                                                                             100 1.52                                                                             100 1.48  216.19                                                                             146.16                                                                              100 29.2                       3  Control mixed                                                                             14.04                                                                              95 1.53                                                                             101 1.84  258.25                                                                             188.22                                                                              129 37.6                          phosphatic fertilizer a                                                       Control mixed                                                                             15.01                                                                             102 1.60                                                                             105 1.75  263.42                                                                             194.39                                                                              133 38.9                          phosphatic fertilizer b                                                    7  Preferred fertilizer A                                                                    15.52                                                                             105 1.65                                                                             109 2.01  312.80                                                                             242.77                                                                              166 48.6                          of the present invention                                                   8  Preferred fertilizer B                                                                    15.69                                                                             107 1.75                                                                             115 1.88  294.56                                                                             224.53                                                                              154 44.9                          of the present invention                                                  10  Preferred fertilizer C                                                                    18.08                                                                             123 1.84                                                                             121 1.85  335.25                                                                             265.22                                                                              182 53.0                          of the present invention                                                  12  Preferred fertilizer D                                                                    19.03                                                                             129 2.08                                                                             137 1.89  358.17                                                                             288.14                                                                              197 57.6                          of the present invention                                                  13  Preferred fertilizer E                                                                    18.95                                                                             129 2.10                                                                             138 2.55  389.36                                                                             313.30                                                                              214 62.7                          of the present invention                                                  __________________________________________________________________________     Notes:                                                                        1. Experiment scale: a/5000 Wagner's pot, triple replication                  2. Test soil: Humus volcanic ash soil                                         3. Test plant: Komatsuna, a kind of Chinese cabbage                           4. Fertilizing weight of phosphoric acid contents: 0.5 g of P.sub.2           O.sub.5 per pot in terms of C--P.sub.2 O.sub.5                                5. Control mixed phosphatic fertilizer composition: 3.94% C--P.sub.2          O.sub.5, 11.95% W--P.sub.2 C.sub.5, and W--P.sub.2 O.sub.5 /C--P.sub.2        O.sub.5 × 100 = 34.2                                                    6. The percentage utilization is determined by absorption/500 × 100                                                                              

As understood from Table 8, the mixed phosphatic fertilizers accordingto the present invention all show significantly higher crop levels ascompared with those shown by fused phosphate only or control mixedphosphatic fertilizers without addition of humic acid. Also, it is shownthat the crop level increases with the quantity of humic acid added tothe feedstock of the phosphatic fertilizer. Further, the mixedphosphatic fertilizers according to the present invention exhibit ahigher fertilizing effect with a relatively low water-solyble phosphoricacid content.

In addition, it is obvious that the mixed phosphatic fertilizersaccording to the present invention all show a remarkably higherpercentage utilization as compared with the control mixed phosphaticfertilizers. Supposedly, such improved features may be attributable tosynergistic effects of citric acid-soluble and water-soluble phosphoricacid contents themselves and as combined with humic acid which itselfhas various soil conditioning effects.

What is claimed is:
 1. A process for producing a mixed phosphaticfertilizer, said process comprising: adding 17.65-100 parts by weight ofhumic acid produced by oxidizing and decomposing ground lignite or browncoal with nitric acid 80-98 parts by weight of fused phosphatecontaining alkaline ingredients to cause said humic acid to react withand complex said alkaline ingredients and form a mixture, then mixingwith said mixture 20-2 parts by weight of a composition selected fromthe group consisting of calcium superphosphate, calciumtriple-superphosphate, phosphoric acid and mixtures thereof, the totalparts by weight of said fused phosphate and said composition being 100,thereby producing said mixed phosphatic fertilizer with stabilizedpredetermined levels of citric acid-soluble and water-soluble phosphoricacid contents.